Manufacturing method for buried insulating layer-type semiconductor silicon carbide substrate

ABSTRACT

A manufacturing method for a buried insulating layer-type semiconductor silicon carbide substrate comprises the step of placing an SOI substrate  100 , which has a surface silicon layer  130  of a predetermined thickness and a buried insulator  120 , in a heating furnace  200  and of increasing the temperature of the atmosphere within heating furnace  200  while supplying a mixed gas (G 1 +G 2 ) of a hydrogen gas G 1  and of a hydrocarbon gas G 2  into heating furnace  200 , thereby, of metamorphosing surface silicon layer  130  of SOI substrate  100  into a single crystal silicon carbide thin film  140.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method for a buriedinsulating layer-type semi conductor silicon carbide substrate and to amanufacturing apparatus thereof.

2. Prior Art

Single crystal silicon carbide (SiC) has been focused on as a materialfor semiconductor devices of the next generation because of itscharacteristics wherein single crystal silicon carbide is excellent inthermal and chemical stability, has a high mechanical strength and isstable when exposed to radiation. In addition, an SOI substrate having aburied insulating layer is excellent in achieving an increase in thespeed of a circuit and a reduction in power consumption and, therefore,is expected to be used as an LSI substrate of the next generation.Accordingly, a buried insulating layer-type semiconductor siliconcarbide substrate having these two characteristics is, therefore,expected to be used as a material for semiconductor devices.

At present, however, a manufacturing method for a buried insulatinglayer-type semiconductor silicon carbide substrate having thecharacteristics of single crystal silicon carbide and an SOI substratehas not yet been established.

As for a method for forming a single crystal silicon carbide thin filmon a silicon substrate, a plasma-type vapor phase reaction, or the like,for example, maybe carried out on a silicon substrate and it is possibleto apply such a technique to an SOI substrate so that a single crystalsilicon carbide thin film is formed on the SOI substrate. In addition,at present, the film thickness of the surface silicon layer in an SOTsubstrate exceeds 50 nm.

There is a problem with a semiconductor substrate that has beenmanufactured according to a method for forming a single crystal siliconcarbide thin film on an SOI substrate wherein a silicon layer isintervened between the single crystal silicon carbide thin film and theburied insulator. A problem arises wherein such a silicon layerintervened between a single crystal silicon carbide thin film and aburied insulator diffuses into the single crystal silicon carbide thinfilm on the surface of the substrate during a heat treatment in a laterprocess leading to the deterioration of the physical characteristicsthereof. In addition, the desired structure wherein silicon carbide isformed on the buried insulator is not gained.

In addition, a film formation process must be carried out in a highvacuum according to a method for forming a single crystal siliconcarbide thin film on an SOI substrate by means of a plasma-type vaporphase reaction, or the like, and, therefore, a manufacturing apparatushaving a complex structure is required. A problem wherein the cost forthe formation of a single crystal silicon carbide thin film is increasedis of course involved with such a manufacturing apparatus due to itscomplex structure.

In addition, in the case of an SOI substrate having a surface siliconlayer of which the film thickness exceeds 10 nm, the metamorphoseedsingle crystal silicon carbide thin film locally causes nucleus growthleading to the formation of grains and, thereby, the surface of thesubstrate becomes coarse, bringing about an unfavorable condition.

SUMMARY OF THE INVENTION

The present invention is provided in view of the above describedsituation and a purpose thereof is to provide a manufacturing methodfor, and a manufacturing apparatus of, a buried insulating layer-typesemiconductor silicon carbide substrate which allows the formation of asingle crystal silicon carbide thin film on an SOI substrate at a lowcost and in a feasible manner.

A manufacturing method for a buried insulating layer-type semiconductorsilicon carbide substrate according to the present invention is providedwith: the first step of placing an SOI substrate having a surfacesilicon layer of which the film thickness is no greater than 10 nm andhaving a buried insulator in a heating furnace and of increasing thetemperature of the atmosphere within the heating furnace while supplyinga mixed gas of a hydrogen gas and a hydrocarbon gas into the abovedescribed heating furnace so that the surface silicon layer of the abovedescribed SOI substrate is metamorphoseed into a single crystal siliconcarbide thin film; the second step of depositing a carbon thin film onthe above described single crystal silicon carbide thin film byexcessively carrying out the above described first step; the third stepof replacing the above described mixed gas with an inert gas wherein anoxygen gas is mixed in a predetermined ratio and of heating the abovedescribed SOI substrate up to 550° C., or higher, so that the abovedescribed carbon thin film is removed through etching; the fourth stepof replacing the above described inert gas, wherein an oxygen gas ismixed, with a pure inert gas, wherein no oxygen gas is mixed, and ofincreasing the temperature of the atmosphere within the above describedheating furnace up to a predetermined temperature; and the fifth step ofsupplying a hydrogen gas and a silane-based gas into the heating furnaceunder the condition wherein the above described predeterminedtemperature of the atmosphere is maintained so that a new single crystalsilicon carbide thin film is made to glow on the single crystal siliconcarbide thin film on the surface of the above described SOI substrate.

In addition, a manufacturing apparatus of a buried insulating layer-typesemiconductor silicon carbide substrate according to the presentinvention is provided with a heating furnace wherein an SO substratehaving a surface silicon layer of which the film thickness is no greaterthan 10 nm and having a buried insulator is placed and which has aheating means for heating the SOI substrate and with a gas supply meansfor supplying a variety of gases into this heating furnace and the abovedescribed gas supply means can supply, at least, a hydrogen gas, ahydrocarbon gas, an oxygen gas, an inert gas and a silane-based gas intothe heating furnace.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F are schematic views showing the respective steps of themanufacturing method for a buried insulating layer-type semiconductorsilicon carbide substrate according to an embodiment of the presentinvention; and

FIG. 2 is a schematic view of a manufacturing apparatus formanufacturing a buried insulating layer semiconductor silicon carbidesubstrate for carrying out a manufacturing method for a buriedinsulating layer semiconductor silicon carbide substrate according to anembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A, 1B, 1C, 1D, 1E and 1F are schematic views showing therespective steps of a manufacturing method for a buried insulatinglayer-type semiconductor silicon carbide substrate according to anembodiment of the present invention; and FIG. 2 is a schematic view of amanufacturing apparatus for manufacturing a buried insulating layer-typesemiconductor silicon carbide substrate according to a manufacturingmethod for a buried insulating layer-type semiconductor silicon carbidesubstrate according to an embodiment of the present invention. Here, thedimensions of the thicknesses of the respective layers in FIG. 1 differfrom the actual proportions for the purpose of convenience ofillustration. In addition, FIG. 1 specifies the surrounding gas in eachstep of the manufacturing method for a buried insulating layer-typesemiconductor silicon carbide substrate.

The manufacturing method for a buried insulating layer-typesemiconductor silicon carbide substrate according to an embodiment ofthe present invention has: the first step of placing an SOI substrate100 having a surface silicon layer 130 of which the film thickness is nogreater than 10 nm and having a buried insulator layer 120 in a heatingfurnace 200 and increasing the temperature of the atmosphere withinheating furnace 200 while supplying a mixed gas (G1+G2) of a hydrogengas G1 and a hydrocarbon gas G2 into the above described heating furnace200 and, thereby, of metamorphoseing surface silicon layer 130 of theabove described SOI substrate 100 into a single crystal silicon carbidethin film 140; the second step of depositing a carbon thin film 150 onthe above described single crystal silicon carbide thin film 140 byexcessively carrying out the above described first step; the third stepof replacing the above described mixed gas (G1+G2) with an inert gas G4wherein an oxygen gas G3 is mixed in a predetermined ratio and, afterthat, of heating the above described SOI substrate 100 up to 550° C., orhigher, so as to remove the above described carbon thin film 150 throughetching; the fourth step of then replacing inert gas G4, wherein theabove described oxygen gas G3 is mixed, with a pure inert gas G4,wherein no oxygen gas G3 is mixed, and of increasing the temperature ofthe atmosphere within the above described heating furnace 200 up to apredetermined temperature; and the fifth step of supplying hydrogen gasGI and a silane-based gas G5 into heating furnace 200 under thecondition wherein the above described predetermined temperature of theatmosphere is maintained so that a new single crystal silicon carbidethin film 160 is made to grow on single crystal silicon carbide thinfilm 140 on the surface of the above described SOI substrate 100.

The above described SOI substrate 100 is gained, as shown in FIG. 1A, byforming a buried insulator layer 120 in a silicon layer 110 as a buriedinsulator and by forming a surface silicon layer 130 having a filmthickness of no greater than 10 nm on this buried insulator layer 120.Here, the crystal orientation in surface silicon layer 130 of this SOIsubstrate 100 is, for example, in the plane direction (111).

Here, the film thickness of surface silicon layer 130 of SOI substrate100 is controlled according to a well-known method such that surfacesilicon layer 130 is oxidized and is etched by hydrofluoric acid, or thelike, so that a desired thickness of the surface silicon layer remains

In addition, an electrical furnace can be used as the above describedheating furnace 200. As shown in FIG. 2, one end of this heating furnace200 has an opening through which an SOI substrate, or the like, isinserted into, or extracted from, the furnace while the other end isconnected to an exhaust means 210 and a heating means 230 such as anelectrical heater is installed a round the furnace wall 220. Inaddition, a gas supply means 300 for supplying a variety of gases intothe furnace is connected to this heating furnace 200. Then, the pressureinside of this heating furnace 200 is equal to atmospheric pressure.

The above described gas supply means 300 has a hydrogen gas supply part310 for supplying a hydrogen gas G1, a hydrocarbon gas supply part 320for supplying a hydrocarbon gas G2, an oxygen gas supply part 330 forsupplying an oxygen gas G3, an inert gas supply part 340 for supplyingan argon gas as an inert gas G4 (including a pure inert gas), asilane-based gas supply part 350 for supplying a silane-based gas G5 anda switching valve 360 to which these gas supply parts 310 to 350 areconnected. This gas supply means 300 is connected to the above describedheating furnace 200 via a supply tube 370.

<First Step> (See FIG. 1B)

The above described SOI substrate 100 is placed inside of heatingfurnace 200 and a mixed gas (G1+G2), wherein hydrocarbon gas G2 is mixedwith hydrogen gas G1 so that the ratio of the hydrocarbon gas becomes 1volume %, is supplied into heating furnace 200 in this first step. Inaddition, simultaneously as this supply of mixed gas (G1+G2), thetemperature of the atmosphere within heating furnace 200 is heated up to1200° C. to 1405° C. As a result of this application of heat, surfacesilicon layer 130 of SOI substrate 100 is metamorphoseed to singlecrystal silicon carbide thin film 140. That is to say, surface siliconlayer 130 of SOI substrate 100 is metamorphoseed to single crystalsilicon carbide thin film 140 in this first step.

The above described single crystal silicon carbide thin film 140 isgained by metamorphoseing surface silicon layer 130 and, therefore, thefilm thickness of single crystal silicon carbide thin film 140 becomesequal to the film thickness of surface silicon layer 130. That is tosay, the film thickness of single crystal silicon carbide thin film 140can be arbitrarily controlled according to the film thickness of surfacesilicon layer 130 of SOI substrate 100.

Here, the above described hydrogen gas G1 is a carrier gas and a propanegas is utilized as hydrocarbon gas G2. In the case that the amount ofsupply of hydrogen gas G1 from hydrogen gas supply part 310 is 1000cc/min, for example, the amount of supply of hydrocarbon gas G2 fromhydrocarbon gas supply part 320 is adjusted to be 10 cc/min.

<Second Step> (See FIG. 1C)

The above described first step is excessively carried out so that carbonthin film 150 is deposited on the above described single crystal siliconcarbide thin film 140 in this second step. The above described carbonthin film 150 is deposited by continuing the above described first stepfor a period of time of, for example, from several minutes to severalhours.

<Third Step> (See FIG. 1D)

In this third step, mixed gas (G1+G2) of hydrocarbon gas G2 suppliedfrom the above described hydrocarbon gas supply part 320 and of hydrogengas G1 supplied from hydrogen gas supply part 310 is replaced with inertgas G4, wherein oxygen G3 is mixed in a predetermined ratio and, then,the above described SOI substrate 100 is heated up to no less than 550°C., for example, approximately 650° C. so that the above describedcarbon thin film 150 is etched and removed. An argon gas, for example,is used as the above described inert gas G4. In addition, as for oxygengas G3 mixed with this inert gas G4, in the case that the amount ofsupply of inert gas G4 from inert gas supply part 340 is 1000 cc/min,for example, the amount of supply of oxygen gas G3 from oxygen gassupply part 330 is adjusted to 100 cc/min.

At the same time when inert gas G4 mixed with this oxygen gas G3 issupplied, SOI substrate 100 is heated up to approximately 650° C. bymeans of heating means 230. This condition is maintained for a period oftime of from several minutes to several hours.

Carbon thin film 150 formed on the surface of SOI substrate 100 ischanged to a carbon dioxide gas as a result of a chemical reaction ofC+O₂→CO₂. Thereby, carbon thin film 150 is etched and removed. Here,this carbon dioxide gas is released to the outside of heating furnace200 by means of exhaust means 210.

<Fourth Step> (See FIG. 1E)

In this fourth step, the above described inert gas G4, wherein an oxygengas is mixed, is replaced with a pure inert gas G4 wherein no oxygen gasis mixed and the temperature of the atmosphere within the abovedescribed heating furnace 200 is increased up to a predeterminedtemperature. Here, a pure argon gas is utilized as the above describedpure inert gas G4. A purpose of the replacement of the gas withinheating furnace 200 with pure inert gas G4 in this fourth step is toavoid the risk of an explosive reaction of a methyl silane gas with anoxygen gas when silane-based gas G5 is utilized in the, subsequent,fifth step.

As for the above described temperature of the atmosphere within heatingfurnace 200, 500° C. to 1405° C. is appropriate.

Here, the above described pure inert gas G4 is supplied to heatingfurnace 200 by stopping the supply of oxygen gas G3 that has beensupplied to heating furnace 200 in the above described third step and bycontinuing the supply of inert gas G4.

<Fifth Step> (See FIG. 1F)

In this fifth step, hydrogen gas G1 is supplied from hydrogen gas supplypart 310 into heating furnace 200 and silane-based gas G5 is suppliedfrom silane-based gas supply part 350 into heating furnace 200,respectively, under the condition wherein the above describedpredetermined temperature (500° C. to 1405° C.) of the atmosphere ismaintained so that new single crystal silicon carbide thin film 160 ismade to grow on single crystal silicon carbide thin film 140 on thesurface of the above described SOI substrate 100.

As the above described silane-based gas G5, for example, a methyl silanegas is used. Silicon is generated as a result of decomposition of thismethyl silane gas and is reacted with carbon in single crystal siliconcarbide thin film 140 and, thereby, an additional single crystal siliconcarbide thin film 160 is formed on single crystal silicon carbide thinfilm 140.

Here, as the above described silane-based gas G5, a monosilane gas, adisilane gas, a dimethylsilane gas, a dichlorosilane gas, or the like,in addition to the methyl silane gas can be utilized.

A buried insulating layer-type semiconductor silicon carbide substratehaving single crystal silicon carbide thin films 140 and 160 can bemanufactured in the above described manner.

Here, though hydrogen gas G1 is supplied from hydrogen gas supply part310, hydrocarbon gas G2 is supplied from hydrocarbon gas supply part320, oxygen gas G3 is supplied from oxygen gas supply part 330, inertgas G4 (including a pure inert gas) is supplied from inert gas supplypart 340 and silane-based gas G5 is supplied from silane-based gassupply part 350, respectively, in the above described embodiment, mixedgas (G1+G2) required for the first step may be prepared in advance bymixing hydrogen gas G1 and hydrocarbon gas G2 in a predetermined ratio,the mixed gas required for the third step may be prepared in advance bymixing inert gas G4 and oxygen gas G3 in a predetermined ratio and thehydrogen gas and silane-based gas required for the fifth step may bemixed in advance in a predetermined ratio.

Here, it can be said that the type of system wherein a variety of gasesare separately supplied is more flexible, from a point of view of thefeasibility of altering the mixture ratio of the various gases in orderto cope with a variety of chemical reactions, than the type of systemwherein a mixed gas prepared in advance by mixing a variety of gases ina predetermined ratio is supplied.

The manufacturing method for a buried insulating layer-typesemiconductor silicon carbide substrate according to the presentinvention has the step of placing an SOI substrate, having a surfacesilicon layer of which the film thickness is no greater than 10 nm andhaving a buried insulator, in a heating furnace and of increasing thetemperature of the atmosphere within the heating furnace while supplyinga mixed gas of a hydrogen gas and of a hydrocarbon gas into the abovedescribed heating furnace so that the surface silicon layer of the abovedescribed SOI substrate is metamorphoseed into single crystal siliconcarbide thin film.

Therefore, a single crystal silicon carbide thin film can be formeddirectly above a buried oxide layer according to this manufacturingmethod without an intervention of a silicon layer, which has caused aproblem in a conventional plasma-type vapor phase reaction method, orthe like, between the single crystal silicon carbide thin film and theburied oxide layer. There fore, a buried insulating layer-typesemiconductor silicon carbide substrate manufactured according to thismanufacturing method solves the conventional problems such as occurrenceof a variety of defects, and a coarse interface, in the interfacebetween the single crystal silicon carbide thin film and the siliconlayer located beneath the single crystal silicon carbide thin film. Inaddition, this manufacturing method solely requires a simple heatingfurnace, such as an electrical furnace, and it is not necessary tomaintain a high vacuum as in a prior art and, therefore, thismanufacturing method can contribute to the simplification of themanufacturing apparatus and of the manufacturing process and, as aresult, can contribute to reduction in manufacturing costs.

In addition, when the film thickness of the surface silicon layer is nogreater than 10 nm, unlike the case of a film thickness of no less than10 nm, a coarse surface due to the occurrence of grains caused by localnucleus growth in single crystal silicon carbide is eliminated, so thatan excellent surface condition can be gained.

1. A manufacturing method for a buried insulating layer-typesemiconductor silicon carbide substrate, characterized in comprising:the first step of placing an SOI substrate, which has a surface siliconlayer of a predetermined thickness formed on top of an insulating layerburied inside the substrate, in a heating furnace and of increasing thetemperature of the atmosphere within the heating furnace while supplyinga mixed gas of a hydrogen gas and of a hydrocarbon gas into said heatingfurnace and, thereby, of metamorphosing the surface silicon layer ofsaid SOI substrate into a single crystal silicon carbide thin film; thesecond step of depositing a carbon thin film on said single crystalsilicon carbide thin film by excessively carrying out said first step;the third step of replacing said mixed gas with an inert gas wherein anoxygen gas is mixed in a predetermined ratio and of heating said SOIsubstrate up to 550° C., or higher, so that said carbon thin film isremoved through etching; the fourth step of replacing said inert gaswherein an oxygen gas is mixed with a pure inert gas into which nooxygen gas is mixed and of increasing the temperature of the atmospherewithin said heating furnace up to a predetermined temperature; and thefifth step of making a new single crystal silicon carbide thin film growon the single crystal silicon carbide thin film on the surface of saidSOI substrate by supplying a hydrogen gas and a silane-based gas intothe heating furnace under the condition wherein said predeterminedtemperature of the atmosphere is maintained.
 2. The manufacturing methodfor a buried insulating layer-type semiconductor silicon carbidesubstrate according to claim 1, characterized in that the surfacesilicon layer of said predetermined thickness has a film thickness of 10nm, or less.
 3. The manufacturing method for a buried insulatinglayer-type semiconductor silicon carbide substrate according to claim 1,characterized in that said predetermined temperature is in a range offrom 500° C. to 1405° C.
 4. The manufacturing method for a buriedinsulating layer-type semiconductor silicon carbide substrate accordingto claim 1 or 2, characterized in that said sequential reactions arecarried out under an atmospheric pressure.